Arrangement in a movable grate

ABSTRACT

A movable grate comprising a number of grate steps which are arranged adjacent each other, partly overlap one another and are pivotable around an axis extending in the longitudinal direction of said grate step, and which are pivotably mounted outside shield members (7, 10) which in lateral direction enclose a combustion chamber, end plates (5) being rigidly secured to the ends of the grate steps and swingable therewith, the end plates being aligned with and fitted in openings in the shield members. The novel matter of the invention resides in that portions (10) of the shield members having such openings aligned with the end plates (5), are displaceably mounted relative to adjoining shield members (7) in the direction of the grate step axis, and that the shield portions (10) which outwardly sealingly engage adjoining shield members (7) and inwardly sealingly engage the end plates (5), are in the direction of said axis rigidly secured to the grate step shaft.

The present invention relates to an arrangement of the type stated inthe preamble of the claim.

In incinerators, especially for refuse and the like, it is importantthat the pressure drop through the grate is carefully supervised. It isequally important that the distribution of air across the entire grateis as uniform as possible to prevent that a strong through-flow of airoccurs at some locations, while at other locations in which the fuellayer is compact, practically no combustion air passes.

In movable grate incinerators, preferably such as described in Swedishpatent specifications 315,679, 316,559 and 338,125, the grate is made upof a number of mutually movable and, more precisely, tiltable steps,each step consisting of a number of bars which are laterallyinterconnected and supported by a common shaft. Each end of such a stepis provided with an end plate adapted to be fitted in an opening in thefixed side shields of the grate. To allow relative pivotal movement ofthe grate steps partly overlapping one another, the front and the rearedges of the step formed by the grate bars extend beyond the associatedend plate and closely follow the side shield as the grate steps move. Inthe prior art design, a space outside the side shield is used as a ductfor secondary air which is blown out at the upper edge of the sideshield after having cooled the outside of the side shield and the endplates. This amount of secondary air constitutes part of the amount ofair which is supplied under the grate as primary combustion air. Thecooling efficiency thus depends to some extent on the amount of primaryair which is injected.

Since the length of the shaft changes under the action of heat, the endplates and the outermost grate rods are displaced relative to the sideshields, for which reason a free space must be left between theoutermost grate rods and the side shields and also at the periphery ofthe end plates so as to prevent mechanical contact with the side shieldsand ensuing wear, when the shaft expands. However, these free spaces,although small in themselves, interfere with air supply and pressuredrop, when the total area of the free spaces along the grate is so largethat the intended air flow cannot be maintained. The air takes theeasiest way, i.e. when the free spaces are "large" along the edges ofthe grate surface where also the fuel layer, as a rule, is thinner thanin the centre, and consequently the supply of air along the centre partof the grate will be insufficient, when the grate temperature is low.When the grate has become heated, the grate step shafts have expandedand the free spaces have been substantially eliminated.

The invention aims at completely obviating the shortcomings which arecaused by the heat expansion and contraction of the grate step shaftsand affect the air supply.

The novel features of the invention are stated in the claims.

An embodiment will now be described with reference to the accompanyingschematic drawings in which

FIG. 1 is a cross-sectional view of one side wall of the incinerator inparallel with the grate step shaft, and

FIG. 2 shows, partly in section radially through the grate step shaftand on a smaller scale, one side of the incinerator as seen from theinside.

One end of the grate step shaft is designated 1, the shaft being mountedin a manner not described in detail in a grate frame (not shown) bymeans of a bearing 2 allowing axial movement of the grate shaft.Adjacent the bearing, cup springs are arranged to position the shaft,and a sealing ring enclosing the cup springs. The grate shaft portion 3extending across the incinerator and radially offset in a crank-likemanner relative to the shaft ends 1, carries a number of grate bars 4forming the grate steps. Adjacent the outermost grate bar 4', an endplate 5 is screwed to the cranked shaft, said end plate following themovement of the grate step. The lower portion of the plate is formed bythe flange coupling between the cranked shaft and the centre part.

The side wall of the incinerator is formed by a brick lining 7 supportedby a beam 6 and made up of different grades of refractory brick, thebrick having the highest resistance and slag-repellency facing thecombustion chamber, or the wall of the incinerator consists of elongatetubes which are welded together and coated with refractory brick. Underthe grate, funnels are arranged for collecting material falling throughthe grate and for injecting the primary combustion air.

Previously, use has been made of shield members connected with the endplates 5 and fixedly mounted on the adjoining wall portions, said shieldmembers defining posteriorly situated secondary air ducts and connectingwith the ends of the grate bars 4 and the periphery of the end plates 5by means of fixed free spaces of the type mentioned above.

The novel matter of the invention resides in that shield portions 10included in the side shield and connected with the end plates 5 are, inthe direction of the axis extending in the longitudinal direction of thegrate step, rigidly secured to the grate step shaft 1 and provided withone or more labyrinth-shaped grooves and ribs 11 along the edge facinginwardly towards the end plate 5, and that the end plates 5 are providedalong their periphery with one or more complementarily designed groovesand ribs 12. As a result, the shield portions 10 will at all times takea fixed position relative to the end plates 5, thereby to enable a veryclose fit in the labyrinth-shaped joint between the plate and the shieldportion.

In the embodiment shown, a further, axially nondisplaceable bearing 13is mounted on the shaft 1 beyond the supporting bearing 2 and carries arigid plate 14. Rigid arms 15 of adjustable length extend from thebearing 13 to a yoke-shaped member 16 supporting the shield portions 10.The upper portion of the member 16 is provided with a hinge-like fitting17 adapted to cooperate with a hook-shaped projection 18 attached to theshield portion 10, while a bolt connection 19 is arranged at the lowerportion. The shield portion can thus be hooked on and pivoted downwardsto be screwed in position.

When the shaft 1, 3 expands, the end plate 5 is moved to the left inFIG. 1 relative to circumjacent stationary portions of the incineratorwall, i.e. the components 6, 7 and 9, respectively. Since the shieldportions 10 are rigidly connected with the shaft 1 via the arms 15, theywill participate in the axial movement and follow the end plates.

On the yoke-shaped member 16, there is mounted a box or cassette 20 madeof metal sheet and abutting, with close fit, flange projections 21 atthe side of the shield portions facing the flange projections. Thecassette serves as a duct 21 for the cooling air intended for the shieldportions 10 and the end plates 5. The cassette can be formed with aconnection to the neighbouring cassettes, such that all cassettesfunction as a long duct over the entire length of the grate. Thecassette can also be formed without connection to the neighbouringcassettes, such that the cooling air is supplied separately to eachcassette. The inlet and outlet ducts for the cooling air are designated22 and 23, respectively.

The stationary partition 24 included in the grate frame is provided withguide means 25 for the arms 15 and can define an outer duct 26 for thecooling air which cools primarily the bearing 2 and the associated cupsprings 27 and also the end of the shaft portion 3. The duct 21 and alsothe duct 26, if any, form a genuine cooling duct, and the air passingtherethrough will not, like before, flow into the combustion chamber assecondary air. This means that, independently of the supply ofcombustion air, adequate cooling of the end plates, shield portions andshaft ends will always be ensured, which, for example during thecombustion stages when the supply of secondary air has been reduced, hasnot been possible in prior art incinerators.

What is claimed is:
 1. An arrangement in a movable grate comprising anumber of grate steps arranged adjacent each other, partly overlappingeach other and preferably formed of grate bars mounted adjacent eachother on a shaft (1,3), each grate step being pivotable around an axisextending in the longitudinal direction of the grate step, and beingpivotably mounted outside shield members (7,10) which in lateraldirection enclose a combustion chamber the bottom of which is formed ofthe grate (4,4') having combustion air passages, end plates beingrigidly secured to the ends of each grate step and swingable therewith,the end plates (5) being aligned with and fitted in openings in saidshield members, characterised in that portions (10) of the shieldmembers having such openings aligned with said end plates (5), aredisplaceably mounted relative to adjoining shield members (7) in thedirection of the grate step axis, and that said shield portions (10)which outwardly sealingly engage adjoining shield members (7) andinwardly sealingly engage said end plates (5), are in the direction ofsaid axis rigidly secured to the grate step shaft which is pivotablerelative to said shield member portions such that the intended tightsealing engagement between said end plates (5) and ajoining shieldmember portions (10) is maintained independently of any temperatureresponsive variation in the length of said grate step and thus of saidshaft (1,3) and said end plates (5).
 2. The arrangement as claimed inclaim 1, characterised in that the shield member portions (10) whichconnect with said end plates (5) and are displaceable along with theshaft are axially rigidly connected, via adjustable arms (15), with asupport means which is arranged at each end of said shaft (1) on bothsides of said grate and which, in turn, is supported by the shaft 1 bymeans of an axially nondisplaceable bearing (13).
 3. The arrangement asclaimed in claim 1 characterised in that the outwardly facing edges ofsaid end plates (5) and the adjoining opposing edges of the movableshield portions (10) are provided with complementary zig-zag surfaces(11,12) forming a labyrinth-shaped seal.
 4. The arrangement as claimedin claim 1, characterised in that the shield portions (10) which areaxially displaceable along with the shaft (1,3) and the end plates (5),are connected with box- or cassette-shaped means (20) arranged outsidesaid shield portions (10) as seen from the combustion chamber andenclosing said shaft 1, said means (20) defining, together with theexterior of said end plates (5) and said shield portions (10), aduct-shaped space (21) conducting an air flow cooling said end plate (5)and said shield portions.
 5. The arrangement as claimed in claim 2,characterised in that the axially nondisplaceable bearing (13) which,via said arms (15) extending in parallel with the shaft, supports theshield portions (10) displaceable along with said shaft, is arrangedoutside the main bearing (2) of said shaft (1), which is supported bythe grate frame and arranged to allow axial movement of the shaft, andthat said arms (15) extend through guide means arranged in the sideportion of said grate frame, said guide means preventing turning of thedisplaceable shield portions along with the shaft (1,3).